EDP Sciences
Free access
Volume 496, Number 3, March IV 2009
Page(s) 805 - 812
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361/200811312
Published online 30 January 2009
A&A 496, 805-812 (2009)
DOI: 10.1051/0004-6361/200811312

An evolved donor star in the long-period cataclysmic variable HS 0218+3229

P. Rodríguez-Gil1, 2, 3, M. A. P. Torres4, B. T. Gänsicke3, T. Muñoz-Darias2, D. Steeghs3, 4, R. Schwarz5, A. Rau6, and H.-J. Hagen7

1  Isaac Newton Group of Telescopes, Apartado de correos 321, 38700, Santa Cruz de La Palma, Spain
    e-mail: prguez@ing.iac.es
2  Instituto de Astrofísica de Canarias, vía Láctea, s/n, La Laguna, 38205 Santa Cruz de Tenerife, Spain
3  Department of Physics, University of Warwick, Coventry CV4 7AL, UK
4  Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
5  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
6  Caltech Optical Observatories, Mail Stop 105-24, California Institute of Technology, Pasadena, CA 91125, USA
7  Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

Received 7 November 2008 / Accepted 20 January 2009

Context. We present time-resolved spectroscopy and photometry of HS 0218+3229, a new long-period cataclysmic variable discovered within the Hamburg Quasar Survey. It is one of the few systems that allow a dynamical measurement of the masses of the stellar components.
Aims. We combine the analysis of time-resolved optical spectroscopy and R-band photometry with the aim of measuring the mass of the white dwarf and the donor star and the orbital inclination.
Methods. Cross-correlation of the spectra with K-type dwarf templates is used to derive the radial velocity curve of the donor star. An optimal subtraction of the broadened templates is performed to measure the rotational broadening and constrain the spectral type of the donor. Finally, an ellipsoidal model is fitted to the R-band light curve to obtain constraints upon the orbital inclination of the binary system.
Results. The orbital period of HS 0218+3229 is found to be $0.297229661 \pm 0.000000001$ d ( $7.13351186 \pm 0.00000002$ h), and the amplitude of the donor's radial velocity curve is $K_2 = 162.4 \pm
1.4$  ${\rm km~s^{-1}}$. Modelling the ellipsoidal light curves gives an orbital inclination in the range $i = 59^{\circ} \pm
3^{\circ}$. A rotational broadening between $82.4 \pm
1.2$  ${\rm km~s^{-1}}$ and $89.4 \pm 1.3$  ${\rm km~s^{-1}}$ is found when assuming zero and continuum limb darkening, respectively. The secondary star has most likely a spectral type K5 and contributes ~80–85% to the R-band light. Our analysis yields a mass ratio of 0.52 < q < 0.65, a white dwarf mass of $0.44 < M_1 (M_\odot) < 0.65$, and a donor star mass of $0.23 < M_2 (M_\odot) < 0.44$.
Conclusions. We find that the donor star in HS 0218+3229 is significantly undermassive for its spectral type. It is therefore very likely that it has undergone nuclear evolution prior to the onset of mass transfer.

Key words: accretion, accretion discs -- stars: binaries: close -- stars: novae, cataclysmic variables

© ESO 2009